Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.85   7.795%   $191.7134   $191.71   $191.70   $191.70  
  Purchase #2 $51.80   8.313%   $56.1061   $56.11   $56.10   $56.10  
  Purchase #3 $116.64   11.602%   $130.1726   $130.17   $130.15   $130.20  
  Purchase #4 $220.67   3.302%   $227.9565   $227.96   $227.95   $228.00  
  Purchase #5 $132.54   8.147%   $143.338   $143.34   $143.35   $143.30  
  Purchase #6 $193.91   10.575%   $214.416   $214.42   $214.40   $214.40  
  Purchase #7 $65.25   8.273%   $70.6481   $70.65   $70.65   $70.60  
  7 purchase totals = $958.66       $1,034.3507   $1,034.36   $1,034.30   $1,034.30